1. Field of the Invention
This invention relates to a process for producing hydroxylamine, and more particularly, to such process utilizing an ion exchange resin to produce purified, concentrated solutions of hydroxylamine free base.
2. Description of the Related Art
Hydroxylamine is prepared commercially by the Raschig process or variations thereof in which ammonium or sodium nitrite is reacted in aqueous solution with ammonium or sodium bi-sulfite and sulfur dioxide and the resulting disulfonate salts are subsequently hydrolyzed to a solution containing essentially hydroxylammonium sulfate, sulfuric acid, ammonium sulfate and/or sodium sulfate plus minor amounts of the corresponding nitrates. This solution can be used, after neutralization with ammonia, as a source of hydroxylamine or pure hydroxylammonium salts from the mixture.
One method of obtaining pure hydroxylammonium salts consists of using a hydroxylammonium containing mixture to synthesize an oxime from a ketone, separating the oxime from the spent solution and hydrolyzing this oxime with a strong mineral acid to recover hydroxylammonium salt and the ketone which can be recycled. This method uses long periods of heating for the hydrolysis and requires expensive equipment for the separation of the oxime from the spent solution and of the hydroxylammonium salt from the ketone. Moreover, salts of hydroxylamine with weak or oxidizing acids cannot be prepared by this method because these acids either do not effect hydrolysis of oximes or decompose the hydroxylammonium salt formed during hydrolysis. Salts of such acids can be prepared by neutralizing cold solutions of hydroxylamine with the corresponding acid.
Heinz Holsapfel in Z. Anorg. und Allgem. Chemie, Vol. 288, page 28 (1956) describes the preparation of hydroxylamine from hydroxylammonium salts by employing an anion exchange resin in the OH form. This publication does not relate to the separation of hydroxylamine from solutions containing other cations. As disclosed in U.S. Pat. No. 3,508,864 issued Apr. 28, 1970 to Wallace T. Thompson et al., hydroxylammonium perchlorate can be produced either by liberating hydroxylamine from a hydroxylammonium salt by passage through an anion exchange resin and neutralizing with perchloric acid, or by absorbing hydroxylammonium ion an a cation exchange resin and then passing perchloric acid through the resin. This method does not separate hydroxylamine from other cations. A cation exchange method is described by Earl. J. Wheelwright in Industrial Engineering Chemistry Process Design Development, Vol. 16, No. 2 (1977), page 220 for the preparation of hydroxylammonium nitrate. This method does not separate hydroxylamine from other cations and moreover the resulting solution of hydroxylammonium nitrate contains significant amounts of nitric acid.
Other methods for manufacturing, recovering, and concentrating hydroxylamine solutions and hydroxylammonium nitrate are known in the art. U.S. Pat. No. 5,213,784 discloses a process for producing concentrated purified hydroxylammonium nitrate. The process involves admixing nitric acid having a concentration less than about 70% to solutions containing excess hydroxylamine. The process avoids spontaneous decomposition of the product.
U.S. Pat. No. 4,725,360 discloses a process for recovering hydroxylamine from waste water in the form of hydroxylammonium sulfate. The process consists of passing the waste water over a strongly acidic ion exchanger and then eluting hydroxylamine associated with the ion exchanger with sulfuric acid.
U.S. Pat. No. 4,202,765 discloses a method for purifying hydroxylamine using anion exchanger. The process consists of passing a hydroxylamine containing solution across a bed of cationic exchange resin and desorbing absorbed hydroxylamine using a monovalent amine or hydroxide base.
The prior art describes methods for preparing hydroxylamine and hydroxylammonium salts, but there is still a need for a simple, inexpensive, and continuous process for separating hydroxylamine from solutions containing ionic contaminants. There is also a great need for a process that is capable of producing a hydroxylamine solutions containing essentially no anion impurities such as sulfates.